Message-ID: <76bec0e9-3d80-469b-8666-06f1b639facb@quicinc.com>
Date:   Tue, 5 Sep 2023 08:20:32 +0530
From:   Om Prakash Singh <quic_omprsing@...cinc.com>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>
CC:     <neil.armstrong@...aro.org>, <konrad.dybcio@...aro.org>,
        <agross@...nel.org>, <andersson@...nel.org>, <conor+dt@...nel.org>,
        <davem@...emloft.net>, <devicetree@...r.kernel.org>,
        <herbert@...dor.apana.org.au>, <krzysztof.kozlowski+dt@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <marijn.suijten@...ainline.org>,
        <robh+dt@...nel.org>, <vkoul@...nel.org>
Subject: Re: [PATCH] crypto: qcom-rng: Add hwrng support



On 9/1/2023 8:16 PM, Bjorn Andersson wrote:
> On Fri, Sep 01, 2023 at 06:45:02PM +0530, Om Prakash Singh wrote:
>> This is follow patch on top of [1]
> 
> This information does not add value to the git history, if you need to
> inform the maintainer that the patch should be applied after some
> in-flight dependency then state so after the "---" line below.
> 
> But, this patch strictly conflicts with [1], so the statement won't make
> sense if this is merged.
> 
>> to add hwrng support for newer platform with trng capability.
> 
> Please rewrite this so that it's clear that the problem you're trying to
> solve with this patch (i.e. the problem description) is that newer
> platforms has trng. Describe how this relates to the existing driver
> (e.g. same/similar hardware interface). State that you purposefully kept
> the crypto interface in place for the new hardware as well (so that it's
> clear that this isn't an accident or oversight).
> 
>>
>> [1] https://lore.kernel.org/lkml/20230824-topic-sm8550-rng-v2-4-dfcafbb16a3e@linaro.org/
>>
>> Signed-off-by: Om Prakash Singh <quic_omprsing@...cinc.com>
>> ---
>>   drivers/crypto/qcom-rng.c | 72 ++++++++++++++++++++++++++++++++++-----
>>   1 file changed, 63 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/crypto/qcom-rng.c b/drivers/crypto/qcom-rng.c
>> index fb54b8cfc35f..f78ffdcc66ec 100644
>> --- a/drivers/crypto/qcom-rng.c
>> +++ b/drivers/crypto/qcom-rng.c
>> @@ -13,6 +13,7 @@
>>   #include <linux/module.h>
>>   #include <linux/of.h>
>>   #include <linux/platform_device.h>
>> +#include <linux/hw_random.h>
> 
> Please keep these sorted, alphabetically.
> 
>>   
>>   /* Device specific register offsets */
>>   #define PRNG_DATA_OUT		0x0000
>> @@ -32,13 +33,18 @@ struct qcom_rng {
>>   	struct mutex lock;
>>   	void __iomem *base;
>>   	struct clk *clk;
>> -	unsigned int skip_init;
>> +	struct qcom_rng_of_data *of_data;
>>   };
>>   
>>   struct qcom_rng_ctx {
>>   	struct qcom_rng *rng;
>>   };
>>   
>> +struct qcom_rng_of_data {
>> +	bool skip_init;
>> +	bool hwrng_support;
>> +};
>> +
>>   static struct qcom_rng *qcom_rng_dev;
>>   
>>   static int qcom_rng_read(struct qcom_rng *rng, u8 *data, unsigned int max)
>> @@ -70,7 +76,7 @@ static int qcom_rng_read(struct qcom_rng *rng, u8 *data, unsigned int max)
>>   		}
>>   	} while (currsize < max);
>>   
>> -	return 0;
>> +	return currsize;
>>   }
>>   
>>   static int qcom_rng_generate(struct crypto_rng *tfm,
>> @@ -79,7 +85,8 @@ static int qcom_rng_generate(struct crypto_rng *tfm,
>>   {
>>   	struct qcom_rng_ctx *ctx = crypto_rng_ctx(tfm);
>>   	struct qcom_rng *rng = ctx->rng;
>> -	int ret;
>> +	int ret = -EFAULT;
> 
> This initialization is useless, the very first thing you do with ret is
> to overwrite it with the return value of clk_prepare_enable().
> 
>> +	int read_size = 0;
> 
> Similarly, the first use of this variable is an assignment. And "ret"
> was a good, short, variable name.
> 
>>   
>>   	ret = clk_prepare_enable(rng->clk);
>>   	if (ret)
>> @@ -87,11 +94,14 @@ static int qcom_rng_generate(struct crypto_rng *tfm,
>>   
>>   	mutex_lock(&rng->lock);
>>   
>> -	ret = qcom_rng_read(rng, dstn, dlen);
>> +	read_size = qcom_rng_read(rng, dstn, dlen);
>>   
>>   	mutex_unlock(&rng->lock);
>>   	clk_disable_unprepare(rng->clk);
>>   
>> +	if (read_size == dlen)
> 
> This function used to return < 0 if qcom_rng_read() returned an error,
> and 0 in all other cases.
> 
> Now you will pass through negative values, you will return 0 if the loop
> in qcom_rng_read() reached "dlen" ("max)", and you will return some
> positive number if the break condition in the loop hit.
> 
> In other words, this is wrong.
> 
>> +		ret = 0;
>> +
>>   	return ret;
>>   }
>>   
>> @@ -101,6 +111,16 @@ static int qcom_rng_seed(struct crypto_rng *tfm, const u8 *seed,
>>   	return 0;
>>   }
>>   
>> +static int qcom_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
>> +{
>> +	int ret;
>> +	struct qcom_rng *qrng;
>> +
>> +	qrng = (struct qcom_rng *)rng->priv;
>> +	ret = qcom_rng_read(qrng, data, max);
>> +	return ret;
> 
> Initialize qrng directly when you define it, drop ret and just return
> qcom_rng_read() directly.
> 
>> +}
>> +
>>   static int qcom_rng_enable(struct qcom_rng *rng)
>>   {
>>   	u32 val;
>> @@ -136,7 +156,7 @@ static int qcom_rng_init(struct crypto_tfm *tfm)
>>   
>>   	ctx->rng = qcom_rng_dev;
>>   
>> -	if (!ctx->rng->skip_init)
>> +	if (!ctx->rng->of_data->skip_init)
>>   		return qcom_rng_enable(ctx->rng);
>>   
>>   	return 0;
>> @@ -157,9 +177,16 @@ static struct rng_alg qcom_rng_alg = {
>>   	}
>>   };
>>   
>> +static struct hwrng qcom_hwrng = {
>> +	.name = "qcom-hwrng",
>> +	.read = qcom_hwrng_read,
>> +	.quality = 1024,
>> +};
>> +
>>   static int qcom_rng_probe(struct platform_device *pdev)
>>   {
>>   	struct qcom_rng *rng;
>> +	const struct qcom_rng_of_data *data;
> 
> Move this one line up, so we maintain the reverse xmas tree.
> 
>>   	int ret;
>>   
>>   	rng = devm_kzalloc(&pdev->dev, sizeof(*rng), GFP_KERNEL);
>> @@ -177,7 +204,8 @@ static int qcom_rng_probe(struct platform_device *pdev)
>>   	if (IS_ERR(rng->clk))
>>   		return PTR_ERR(rng->clk);
>>   
>> -	rng->skip_init = (unsigned long)device_get_match_data(&pdev->dev);
>> +	data = of_device_get_match_data(&pdev->dev);
>> +	rng->of_data = (struct qcom_rng_of_data *)data;
> 
> Why didn't you assign rng->of_data directly?
> 
> Also, of_device_get_match_data() returns a void *, so you should have to
> explicitly cast this.
> 
>>   
>>   	qcom_rng_dev = rng;
>>   	ret = crypto_register_rng(&qcom_rng_alg);
>> @@ -185,6 +213,14 @@ static int qcom_rng_probe(struct platform_device *pdev)
>>   		dev_err(&pdev->dev, "Register crypto rng failed: %d\n", ret);
>>   		qcom_rng_dev = NULL;
>>   	}
> 
> Would be nice with a newline here, to get some separation between the
> "paragraphs".
> 
>> +	if (rng->of_data->hwrng_support) {
>> +		qcom_hwrng.priv = (unsigned long)qcom_rng_dev;
>> +		ret = hwrng_register(&qcom_hwrng);
>> +		if (ret) {
>> +			dev_err(&pdev->dev, "Register hwrng failed: %d\n", ret);
>> +			qcom_rng_dev = NULL;
> 
> You're leaving the rng registered with crypto here. Not sure if that
> will result in a use after free, or just a NULL pointer dereference -
> but it's not good either way.
> 
>> +		}
>> +	}
>>   
>>   	return ret;
>>   }
>> @@ -193,11 +229,29 @@ static int qcom_rng_remove(struct platform_device *pdev)
>>   {
>>   	crypto_unregister_rng(&qcom_rng_alg);
>>   
>> +	if (qcom_rng_dev->of_data->hwrng_support)
>> +		hwrng_unregister(&qcom_hwrng);
> 
> Why not use devm_hwrng_register() above instead? Then you wouldn't have
> to unregister it here.
> 
>> +
>>   	qcom_rng_dev = NULL;
>>   
>>   	return 0;
>>   }
>>   
>> +struct qcom_rng_of_data qcom_prng_of_data = {
>> +	.skip_init = false,
>> +	.hwrng_support = false,
>> +};
>> +
>> +struct qcom_rng_of_data qcom_prng_ee_of_data = {
>> +	.skip_init = true,
>> +	.hwrng_support = false,
>> +};
>> +
>> +struct qcom_rng_of_data qcom_trng_of_data = {
>> +	.skip_init = true,
> 
> Can you please confirm that it's appropriate to name this "trng" without
> the "-ee" suffix. Should all trng instances (v2 and v3) skip
> initialization?
All trng supported platform needs to skip initialzation.
we don't need to have both "trng-ee" and "trng".
If "trng-ee" is prefer we shold update it in patch [1] it itself,

> 
>> +	.hwrng_support = true,
>> +};
>> +
>>   static const struct acpi_device_id __maybe_unused qcom_rng_acpi_match[] = {
>>   	{ .id = "QCOM8160", .driver_data = 1 },
>>   	{}
>> @@ -205,9 +259,9 @@ static const struct acpi_device_id __maybe_unused qcom_rng_acpi_match[] = {
>>   MODULE_DEVICE_TABLE(acpi, qcom_rng_acpi_match);
>>   
>>   static const struct of_device_id __maybe_unused qcom_rng_of_match[] = {
>> -	{ .compatible = "qcom,prng", .data = (void *)0},
>> -	{ .compatible = "qcom,prng-ee", .data = (void *)1},
>> -	{ .compatible = "qcom,trng", .data = (void *)1},
>> +	{ .compatible = "qcom,prng", .data = &qcom_prng_of_data },
>> +	{ .compatible = "qcom,prng-ee", .data = &qcom_prng_ee_of_data },
>> +	{ .compatible = "qcom,trng", .data = &qcom_trng_of_data },
> 
> So, should this be qcom,trng or qcom,trng-ee?
> 
> 
> Where is your devicetree binding patch?
DT binding patch is submitted by Neil [1]

I will address all other review comments in next patch version.

[1] 
https://lore.kernel.org/lkml/20230824-topic-sm8550-rng-v2-4-dfcafbb16a3e@linaro.org/

> 
> Regards,
> Bjorn

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